Over 1000 practitioners undertake hair transplantation in the United States, principally utilizing conventional techniques.
Under a conventional approach a scalpel or trephine punch is used to graft and implant circular or rectangular hair bearing areas. Typically, hair bearing areas from the rear of the scalp containing one or several hair follicles are removed and transplanted to the alopecic (bald) site.
These hair bearing tissue samples are then manually positioned in recipient sites consisting of previously prepared craters or incisions in the tissue. Such historical surgical approaches have utilized round and slit shaped recipient site preparation. Round recipient sites are prepared with circular punches, while slit-shaped recipient sites are prepared with surgical scalpels. Round grafts have been favored for higher graft density, while slit grafts present a more natural profile. Hair may be transplanted as micrografts containing 1-2 hairs or as minigrafts containing 4-5 hairs. The typical recipient site will be prepared to a tissue depth of approximately 3 mm.
Several disadvantages attend conventional hair transplantation techniques. Round grafts can appear `clumpy` and unnatural, while slit grafts can compress the transplanted hair, creating a raised, unnatural appearance, especially with darker, coarser hair. This is a consequence of the fact that the scalpel is not removing a section of alopecic scalp, but rather creating a gaping slit, of typical length 5-6 mm. Further, the compression may be associated with hypoxia and hair growth failure.
It has been suggested (Unger, W. P., Journ. Derm. Surg. Oncol., 20, 8, 1994) that the precise removal of a section of alopecic scalp tissue would eliminate any compression, while simultaneously presenting the potential for a higher density of transplanted hair, since alopecic scalp would actually be removed. These factors, together with the potential reduction of operative bleeding, led to the initiation of trials in 1992 of laser induced slit transplant preparation using mid infra-red CO.sub.2 lasers emitting at 10.6 .mu.m. Such laser assisted hair transplantation has been reported using carbon dioxide lasers in superpulsed or scanned mode. Under such techniques, hair bearing sites are removed and prepared as before, while the laser is used to prepare the recipient site.
In the first reported study (Unger, W. P., Journ. Derm. Surg. Oncol., 20, 8, 1994), Unger described treatment of a limited number of patients using a superpulsed CO.sub.2 laser, with up to 450 mJ applied at 12-15 Watt average power along a line 0.2 mm wide by 3 mm long. Here, the laser was traced along a series of such interweaving lines, which immediately gape to 0.5 mm, with superficial de-epithelialization and proximal tissue damage. Crater depth was not reported.
While the pulsed CO.sub.2 laser was capable of hemostatic injury, Unger found it useful to increase the applied fluence to create some minimal bleeding, to better retain the transplanted hairs. Bleeding is indicative of the good vascular supply necessary to ensure graft take. In the absence of such, Unger noticed a significant failure rate. Results were acceptable at high fluence levels, although regrowth of hair was delayed by some 2-6 weeks when compared with scalpel slits, probably due to proximal tissue necrosis.
Continuous wave CO.sub.2 lasers have also been used for hair transplantation. Grevelink has described (Grevelink, J. M., Obj. Tech. Oto. Head Neck Surg, 5, 4, 1994) the use of a Sharplan 15 Watt laser with scanner to create a recipient site of diameter 2 mm and depth up to 6 mm. A single patient was so treated, with minimal operative bleeding. A wide zone of coagulative necrosis of width 175 .mu.m was created around the crater. Follow up data has not been published and graft viability is unknown.
The wide zone of hemostasis associated with use of the CO.sub.2 laser is a consequence of the non-optimal choice of wavelength. At the CO.sub.2 laser wavelength of 10.6 .mu.m, tissue absorbs most of the energy within 50 .mu.m, although a wider tissue volume can be affected. This results in wider tissue injury and hemostasis than would be optimal. It is likely that the hemostasis associated with the use of the CO.sub.2 lasers described above will also impair graft take viability, since such hemostasis is associated with a coagulative damage zone around the recipient site. The protracted erythematous period as noted is indicative of the cellular repair and angiogenic processes associated with significant wound formation. As a consequence of this wound formation, transplanted hair follicles may not receive sufficient nourishment during or subsequent to this healing phase.
This document describes a method and apparatus for skin ablation and for the reduction of the adverse effects associated with laser hair transplantation.